1. Field of the Invention
The present invention relates to an electric fan. More specifically, the present invention relates to a novel electric fan using a DC brushless motor for driving an impeller.
2. Description of the Prior Art
An electric fan is disclosed, for example in U.S. Pat. Nos. 3,446,429; 3,481,533 and so on. Since these electric fans are all using an induction motor, a starting torque is small, thus difficulty being encountered in starting at low speed.
When started at low speed, therefore, a starting compensating circuit is required to shift to the low speed after once driven at high speed as disclosed, for example, in Japanese Utility Model Publication No. 46164/1975. Thus, in the conventional electric fan using an induction motor, complicated circuit should be utilized to enable the starting at low speed.
In the conventional electric fan using the induction motor, since torque is small at low speed and the lower limit of the normally driveable speed is high, a so-called ultralow speed driving is impossible.
Moreover, the use of an induction motor increases the outside diameter of the motor and causes the larger proportion of that portion relative to the outside diameter of the impeller, thereby blocking the wind and deteriorating the fan efficiency.